Broadband White-light Emission Research Articles

A novel halide hybrid white light emitter with remarkable structural and emission stability

Addressing the issues of self-absorption effect among different components in traditional white light-emitting diodes (WLEDs) and the high cost associated with rare earth elements, we propose the potential utility of zero-dimensional organic–inorganic metal halide hybrids (0D OIMHs) in white WLEDs fabrication. In this study, we synthesized a novel 0D OIMH, (C5N2H14)ZnCl4, characterized by broadband white light emission. The (C5N2H14)ZnCl4 crystal features a short ultraviolet cutoff situated at 190 nm and emits cold white light with a Color Rendering Index (CRI) of 73 under an excitation wavelength of 260 nm. Furthermore, (C5N2H14)ZnCl4 demonstrates exceptional structural and emission stability in an air atmosphere over a span of three months.

Bulk Coassembly of Zero-Dimensional Heterometallic Halide Hybrids for Broadband White Light Emission and Optical Thermometry

Bulk Coassembly of Zero-Dimensional Heterometallic Halide Hybrids for Broadband White Light Emission and Optical Thermometry

Tunable White Light Emission of a Metal-Organic Framework Based on a Bisquinoxaline Derivative by Introducing Red-Green Cationic Dyes.

The unique structural advantages give metal-organic frameworks (MOFs) a special use as host substrates to encapsulate organic dyes, which would result in specific host-guest composites for white-light phosphors. In this work, an anionic MOF exhibiting blue emission was constructed using bisquinoxaline derivatives as photoactive centers, which could effectively encapsulate rhodamine B (Rh B) and acriflavine (AF) to form an In-MOF ⊃ Rh B/AF composite. By simply adjusting the amount of Rh B and AF, the emitting color of the resulting composite could be easily adjusted. The formed In-MOF ⊃ Rh B/AF composite exhibits broadband white light emission with ideal Commission International ed'Eclairage (CIE) coordinates of (0.34, 0.35), a color rendering index of 80.8, and a moderately correlated color temperature value of 5193.96 K. This strategy can be easily extended to other blue-emitting MOFs and dyes, thus opening up new prospects for the development of white-light-emitting materials.

White-light emission from yttrium iron garnet (YIG)

Single-phase phosphors that emit broadband white-light are needed for white-light-emitting diodes (wLEDs) to reach their full potential. However, it is challenging to achieve broad white-light emission from single-phase materials. Consequently, polycrystalline inorganic bulk compounds that emit white-light sans doping are rare. We report on broadband white-light emission from a well-known garnet compound, i.e., yttrium iron garnet (YIG), without activator-ion doping. Upon near-UV excitation at 370 nm, polycrystalline bulk YIG emits broadband white-light with (1931) Commission Internationale de L’Eclairage (CIE) coordinates as (0.28, 0.35) and correlated color temperature (CCT) as 8029 K. Variable excitation wavelengths ranging from 280 to 600 nm enable color-tunable emission as cyan-white-blue-green-yellow-orange-red, including near-white-light emission for a broad range of excitation from 325 to 390 nm. Moreover, a short lifetime (sub-nanosecond) is obtained, which is desirable for LED and other applications. We demonstrated the propriety of YIG as a single-phase converting phosphor for illumination by fabricating prototype wLEDs using commercial InGaN UV-LED chips (λ = 380 nm) for excitation. The CIE coordinates and CCT of prototype wLEDs were obtained as (0.34, 0.37) and 5284 K, respectively. We believe that the reported findings signify the great potential of YIG as a single-phase white-light-emitting phosphor for broadband emission, which offers a new perspective and a viable approach for the development of wLEDs.

White Light Emission from Single-Component Cs7Cd3Br13:Pb2+,Mn2+ Crystals with High Quantum Efficiency and Enhanced Thermodynamic Stability

Single-component white light emitters are particularly attractive for fabricating economical solid-state devices for display and lighting. Herein, an efficient white light with photoluminescence quantum yields approaching 98% has been obtained in Mn2+ and Pb2+ co-doped Cs7Cd3Br13 crystals. The quantified bonding and nonbonding characters calculated by the crystal orbital Hamilton population analysis demonstrate that the Mn2+ and Pb2+ occupy preferentially in the [CdBr4]2– tetrahedrons rather than the [CdBr6]4– octahedrons in Cs7Cd3Br13. According to the PL spectral characteristic and the theoretical results, the broadband white light emission from Cs7Cd3Br13:Pb2+,Mn2+ crystals is ascribed to the multiple PL origins, i.e., the first self-trapped exciton (STE1) from the intrinsic trapping states of host lattice Cs7Cd3Br13, the d–d transition of Mn2+, and the second self-trapped exciton (STE2) induced by the introduction of Pb2+, respectively. The results calculated by density functional theory reveal that the incorporation of Mn2+ and Pb2+ has significantly improved the thermodynamic stability of the Cs7Cd3Br13 structure with lower defect formation energies, which is verified by the experimental observation in the temperature-dependent PL spectra of the emitting crystals. The findings here provide a new perspective for a single-component white light via creating multiple PL centers in a single matrix as well as help in the elucidation of the preferential site occupancy mechanism of the dopants in different symmetrical units.

Multifunctional dielectric/optical response with broadband white light emission in a hybrid stannic halide crystal

This study investigates dielectric switching response equipped with broadband white-light emission in a single hybrid material (3-methoxypropylamine)2SnCl6.

Exploring the intra-4f and the bright white light upconversion emissions of Gd2O3:Yb3+,Er3+-based materials for thermometry.

Upconversion broadband white light emission driven by low-power near-infrared (NIR) lasers has been reported for many materials, but the mechanisms and effects related to this phenomenon remain unclear. Herein, we investigate the origin of laser-induced continuous white light emission in synthesized nanoparticles (Gd0.89Yb0.10Er0.01)2O3 and a mechanical mixture of commercial oxides with the same composition 89% Gd2O3, 10% Yb2O3, and 1% Er2O3. We report their photophysical features with respect to sample compactness, laser irradiation (wavelength, power density, excitation cycles), pressure, temperature, and temporal dynamics. Despite the sensitizer (Yb3+) and activator (Er3+) being in different particles for the mechanical mixture, efficient discrete and continuous upconversion emissions were observed. Furthermore, the synthesized nanoparticles were developed as primary luminescent thermometers (upon excitation at NIR) in the 299-363 K range, using the Er3+ upconversion 2H11/2 → 4I15/2/4S3/2 → 4I15/2 intensity ratio. They were also operating as secondary ones in the 1949-3086 K, based on the blackbody distribution of the observed white light emission. Our findings provide important insights into the mechanisms and effects related to the transition from discrete to continuous upconversion emissions with potential applications in remote temperature sensing.

Exploring a Stable and Dense 3D Lead Chloride Hybrid with Emission of Self‐Trapped Excitons toward X‐Ray Scintillation

AbstractThe exceptional photophysical properties of 3D organic–inorganic lead halide hybrids (OILHs) endow their significant potential for usage in optoelectronics, which has sparked intense research on novel 3D OILHs and associated applications. However, constructing new 3D OILHs based on large organic cations suffers from tough challenges due to the limitation of the Goldschmidt tolerance factor rule, let alone further explorations of their practical applications. Herein, a brand‐new 3D lead chloride hybrid, (1MPZ)Pb4Cl10·H2O (1, 1MPZ = 1‐methylpiperazine) is reported, featuring a dense 3D lead chloride framework made of the corner‐, edge‐, and face‐shared lead chloride polyhedra. 1 presents a broadband white light emission with a large Stokes shift and a nanosecond photoluminescence lifetime, which originates from radiative recombination of self‐trapped excitons (STEs) induced by the highly distorted structure. Such a reabsorption‐free and fast‐decayed STEs emission coupling with the dense 3D architecture further enables 1 with effective X‐ray scintillation with good sensitivity. Impressively, 1 also shows superior environmental and radiation stability. This study provides a new 3D OILH with appealing luminescence, not only expanding the 3D OILH family but also inspiring the exploitation of their optoelectronic applications.

Up-conversion luminescence and broadband white-light emission in La1-xErxGa0.5Sb1·5O6, Bi1-xErxGeSbO6

In this paper, we first synthesized La1-xErxGa0.5Sb1·5O6 and Bi1-xErxGeSbO6 phosphors with rosiaite structure and studied their spectral luminescent properties. We demonstrated the influence of the matrix composition on the intensity ratio of the Er3+ luminescence bands, due to the transitions from the 2H11/2, 4S3/2, 4F9/2, 4I9/2, and 4 I11/2 excited states to the 4I15/2 ground state upon excitation to the 4I13/2 level. It is shown that the increase in the intensity ratio of the bands corresponding to the 2H11/2 → 4I15/2 and 4S3/2 → 4I15/2 transitions is more pronounced for La1-xErxGa0.5Sb1·5O6 compounds compared to Bi1-xErxGeSbO6. This indicates that the processes of interaction in the studied matrices are different.Along with the luminescence of erbium, broadband thermal white-light emission was detected in highly doped samples after increasing the power density of the exciting radiation with λexc. = 1550 nm. For La1-xErxGa0.5Sb1·5O6 compounds, it occurs at a lower power density than for Bi1-xErxGeSbO6, which may be due to the features of interactions of RE ions with the host, as well as with the particle morphology.

Lead-Free Potassium Alloyed Cs2AgBiBr6: Tunable Optoelectronic Properties and Carrier-Lattice Interaction

The role of the carrier-lattice interaction and associated self-trapped excitons (STEs) in broadband white-light emission in perovskite halides is one of the key aspects when aiming to develop next generation semiconductors for lighting applications. Herein, we provide microscopic insight on optoelectronic properties and electron–phonon interactions in potassium (K+) alloyed Cs2AgBiBr6, while evaluating its potential as a single material tunable light emitter. While K+ partially occupying the Cs+ site leads to blue-light emission at low K+ ion concentrations, a sudden photoluminescence broadening and white-light emission occur at relatively higher alloying concentrations where K+ starts to occupy Ag+ sites. Simulation reveals an anomalous increase in carrier lattice coupling strength (via the Fröhlich mechanism) when K+ replaces Ag+. This along with the increased density of STEs (aided by strong electron–phonon coupling and more octahedral distortion) and induced free exciton (FE) emission is proposed to play a major role behind the observed photoluminescence (PL) broadening and white-light emission. This study should stimulate further research on single material based white-light emitters for next generation solid-state lighting applications.

Highly Stable and Moisture-Immune Monocomponent White Perovskite Phosphor by Trifluoromethyl (-CF3) Regulation.

Halide perovskites are emerging as promising candidates for white light solid state lighting. Nevertheless, there are still challenges of a high water stability, a tunable color temperature, and a high photoluminescence quantum yield (PLQY). Herein, we report hydrophobic, electron-withdrawing trifluoromethyl (-CF3)-modified phenethylamine lead bromide (PEA2PbBr4) with ultrahigh stability in water for >2 months, and the broadband white light emission is illustrated by self-trapped excitons attributed to exciton-phonon coupling that coordinate molecular vibration, lattice distortion, and electrostatic interaction. In particular, by Mn2+ doping, the emission color can be tuned from cold (10237 K) to warm (2406 K), and a greatly enhanced PLQY of ≤87.93% can be achieved. Furthermore, the perovskites also possess an excellent color rendering index (the highest is 94). A monocomponent white light-emitting diode with amazing CIE 1931 coordinates of (0.33, 0.32) is further assembled, demonstrating a luminance of 471.5 cd m-2 at 50 mA and good long-term operation stability after >2 months. This study of highly efficient and stable perovskites with high-quality white light emission will open up new opportunities in solid state lighting.

Zero-Dimensional Hybrid Indium Halides with Efficient and Tunable White-Light Emissions.

Two-dimensional hybrid lead perovskites have attracted a great deal of attention in white-light-emitting diodes, but the serious toxicity of Pb2+ and the limited photoluminescence quantum yield (PLQY) still restrict further optoelectronic application. To address these issues, a new combining photon strategy was proposed to achieve highly efficient broadband white-light emission in a new family of zero-dimensional (0D) indium halides based on an [InCl6]3- octahedron. Remarkably, these 0D halides display dual-band white-light emission derived from the synergistic work of blue- and yellow-light-emitting bands, which can be ascribed to the radiative recombination of bound excitons in organic cations and self-trapped excitons in inorganic anions, respectively, based on spectroscopy and theoretical studies. In-depth first-principles calculation demonstrates that the increased structural deformability effectively improves the PLQY from 7.01% to 18.56%. As a proof of concept, this work provides a profound understanding for advancing the rational design of novel single-component 0D lead-free halides as high-performance white-light emitters.

(Invited) Nanocrystalline Oxide-Based Luminescent Nanophotonic Structures

Light nanoemiters are the cornerstone of photonic integrated applications including displays for consumer products such as phones and smartwatches, and for advanced application such as quantum emitters. In this context it is appealing to have access to a single material platform suitable for tunable wavelength emission, and if possible, that can provide broadband white light emission. Solid state light emitting nanostructures based on Europium ions are a promising solution. When imbedded in a solid they can have two oxidation states Eu3+ or Eu2+ which upon excitation show a either a high purity red emission (associated to the Eu3+ dipole-forbidden intra-4f shell 5D0® 7F2 transition), or a broad emission band in the 450-600 nm spectral region (related to the Eu2+ dipole-allowed 4f6 5d -> 4f7 transitions). Here I will discuss the strategy that our group is following based on europium oxides EuOx, 1/3<x<1, as this approach allows to have a high density of emitters. Moreover, their electric and optical properties can be tuned from the sesquioxide Eu2O3 that is a wide bandgap dielectric that shows the Eu3+ ion related narrow band red emission, to the monoxide EuO that is a semiconductor that shows a wide band white light emission related to the Eu2+ ion. For the nanoemitters we have prepared EuOx nanocrystalline films with high transparency, and in which the coexistence of both oxidation Eu states enables wavelength tunability [1.2]. Finally, recently we have designed 2D hybrid nanoemitters by integrating the EuOx films with metallic metasurfaces in order to induce an enhancement of the emission intensity by selective plasmonic excitation [3].[1] A. Mariscal, A. Quesada, A. Tarazaga Martín-Luengo, Miguel A. García, A. Bonanni, J.F. Fernández and R. Serna, Appl. Surf. Science 456,980 (2018).[2] A. Mariscal-Jiménez, A. Tarazaga Martín-Luengo, B. Galiana, C. Ballesteros, A. Bonanni, J. Martín-Sánchez, R. Serna, J. Phys. Chem. C. 124, 15434–15439 (2020).[3] P. Gomez-Rodriguez, E. Soria, Y. Jin, A. Caño, I. Llorente, A. Cuadrado, A. Mariscal-Jiménez, A. K. Petford-Long, R. Serna and J. Gonzalo, Nanophotonics. 10, 3995–4007 (2021).

All-carbon stretchable and cavity-free white lasers.

Flexible, stretchable, and bendable electronics and optoelectronics have a great potential for wide applications in smart life. An environmentally friendly, cost effective and wide-angle emission laser is indispensable for the emerging technology. In this work, circumvent the challenge issue, cavity-free and stretchable white light lasers based on all carbon materials have been demonstrated by integration of fluorescent carbon quantum dots (CQDs) and crumpled graphene. The typical emission spectrum of the cavity-free laser based on all-carbon materials has a CIE chromaticity coordinate of (0.30, 0.38) exhibiting an intriguing broadband white-light emission. The unprecedented and non-toxic stretchable and white light cavity-free lasers based on all-carbon materials can serve as next-generation optoelectronic devices for a wide range application covering solid-state lighting and future wearable technologies.

Cis/trans-Isomeric Cation Tuning Photoluminescence and Photodetection in 2D Perovskites.

Cationic components in the organic-inorganic hybrid perovskites (OIHPs) play an important role in the arrangement and tilting of the inorganic part that is responsible for semiconducting, luminescent, and photoelectronic properties. Herein, we report two 2D OIHP compounds, (cis-4ACHO)2(H3OBr)PbBr4 (1) and (trans-4ACHO)2(H3OCl)PbBr4 (2) (4ACHO = 4-aminocyclohexanol), showing both photoluminescence (PL) and photodetection (PD) that are tuned by the cis- and trans configurational isomerism of 4ACHO. Crystals of 1 and 2 exhibit similar packing structures but with different crystallographic symmetries. Compound 2 displays a broadband white-light emission with a higher PL efficiency (6.6%) than 1 (2.1%) that emits narrowband blue light while the PD property of 1 is better than 2 with a higher on/off ratio under the same conditions. The PL and PD of the two compounds show a seesaw relationship, which provides a new perspective for understanding the PL and PD properties in OIHPs.

Corrugated 1D Hybrid Metal Halide [C6H7ClN]CdCl3 Exhibiting Broadband White-Light Emission.

Organic-inorganic hybrid metal halides (OIMHs) exhibiting white-light emission are a splendid class of emitters and are regarded as desired phosphors for solid-state lighting applications. Here we report a single-component white-light-emitting hybrid metal halide, namely, [C6H7ClN]CdCl3 (C6H7ClN = 4-(chloromethyl)pyridinium), which features a corrugated 1D anionic double chain composed of edge-shared CdCl6 octahedrons and exhibits broadband white-light emission with a photoluminescence quantum yield of 12.3% under 365 nm UV light irradiation. Density functional theory calculations and temperature-dependent emission spectral analysis unveil that the broadband emission of [C6H7ClN]CdCl3 is ascribed to self-trapped excitons. Moreover, a single-component white-light-emitting diode device with a correlated color temperature of 5214 K and color rendering index of 83.7 can be fabricated via coating [C6H7ClN]CdCl3 on a 365 nm UV light-emitting diode chip. Such a promising luminescent material provides guidance for the design and synthesis of OIMHs with unique structures and desired properties.

Light Emission Enhancement of (C3H10N)4Pb1-xMnxBr6 Metal-Halide Powders by the Dielectric Confinement Effect of a Nanosized Water Layer.

Organic-inorganic hybrid metal halides have been widely studied as a kind of phosphor materials for high-performance white light-emitting diodes. In this paper, a series of organic-inorganic metal-halide (C3H10N)4Pb1-xMnxBr6 powders with different Mn2+ ion doping concentrations were synthesized by mechanochemical methods, giving broadband white light emission with a photoluminescence quantum yield of 36.1% at room temperature, which turn green with a much larger intensity at 80 K. Interestingly, its emission converted from white to red after 100 °C treatments and turned back to white again when exposed to moist air for a while. This emission variation was caused by the adsorbed water layer on the surface of product powders via the dielectric confinement. The red emission from no water powders is identified to occur from the Mn ferromagnetic pair in point-shared octahedral sites, while the broadband white emission originated from the surface water-assisted dielectric confinement and surface polarization which combine the self-trapped excitons and d-d transitions of Mn ions and Mn pairs in the product. Moreover, this white emission can transform into green color at 80 K with a much stronger intensity, caused by the even efficient surface dielectric confinement by the adsorbed frozen water layer. This special compound has the advantages of simple preparation, low cost, and good stability and even contains water molecule in the air, giving a near-perfect white emission, with CIE of (0.33, 0.35) and correlated color temperatures at around 5733 K, which may be used for different applications such as sensing, solid-state lighting, and display.

Broadband white-light emission from a novel two-dimensional metal halide assembled by Pb–Cl hendecahedrons

The abundant selection of organic molecules and inorganic units has allowed for the fabrication of organic–inorganic hybrid metal halides (OIMHs) of various morphologies and crystal structures with controllable molecular dimensions and unique photoelectric properties.

A promising 1D Cd-based hybrid perovskite-type for white-light emission with high-color-rendering index.

A one dimensional (1D) perovskite-type (C6H7NBr)3[CdBr5] (abbreviated 4-BAPC) was synthesized by slow evaporation at room temperature (RT). 4-BAPC crystalizes in the monoclinic system with the space group P21/c. The 1D inorganic chains are formed by corner sharing CdBr6 octahedra. Thermal measurement shows that 4-BAPC is stable up to 190 °C. Optical characterization demonstrates that the grown crystal is an indirect bandgap material with a bandgap value of 3.93 eV, which is consistent with theoretical calculations. The electronic structure, calculated using density functional theory, reveals that the valence band originates from a combination of Br-4p orbitals and Cd-4d orbitals, whereas the conduction band originates from the Cd-5s orbitals. The photoluminescence spectroscopy shows that the obtained material exhibits a broad-band white light emission with extra-high CRI of 98 under λ exc = 380 nm. This emission is mainly resulting from the self-trapped exciton recombinations within the inorganic CdBr6 octahedron, and the fluorescence within the organic conjugated ammonium salt.

Highly efficient broadband white-light emission in two-dimensional semi-conductive hybrid lead chlorides.

White-light emission (WLE) materials based on organic-inorganic hybrid lead halides have drawn considerable attention because of their applications in light-emission equipment. Despite considerable efforts, there is still a lack of two-dimensional (2D) lead-chlorine white-light emitting halides with high photoluminescence quantum efficiency (PLQE). Herein, we report the preparation of a new 2D layered hybrid halide, [DTHPE]Pb4Cl10, which exhibits bright wide-band WLE, a high PLQE of 8.86% and high anti-water stability. To the best of our knowledge, the PLQE of [DTHPE]Pb4Cl10 exceeds that of most 2D lead chlorides. Furthermore, the emission intensity is unchanged even after continuous immersion in water for 7 days. Photoluminescence measurements indicate that the WLE originates from self-trapped excitons. [DTHPE]Pb4Cl10 is a promising visible-blind UV hybrid halide owing to its excellent photoelectric response. [DTHPE]Pb4Cl10 is an effective white-light emitting material for display applications. The coexistence of a high performance visible-blind UV response and high efficiency white-light emission provides attractive possibilities for potential applications in the multifunctional photoelectronic field.